This invention relates to a cable for use in optical communication as an indispensable communication means for the highly informationalized society.
With the recent switching over to the informationalized society, the surrounding technologies are also in rapid development. Among others, optical communication has many features such as a distinguished transmission capacity, being free from communication troubles due to electric discharge, lightning, electromagnetic induction, etc., and no use of precious copper, as compared with the electrical communication based on the conventional copper wires. Therefore optical communication is highly expected as an information transmission means.
Optical fibres made from quartz, glass, and transparent synthetic resin are used for strands. The former two are very brittle, and damaged or broken by an impact force suddenly applied thereto during the handling, and thus are usually used after coating with synthetic resins such as silicone resin, etc.
To prevent damage and breakage of the strands including the optical fibers based on the transparent synthetic resin due to elongation during the handling, a tension-resistant material or strength member is provided around the strand of optical fibers, and the tension-resistant material is further coated with a synthetic resin. An impact force applied thereto during the handling is borne on the tension-resistant material. As a tension-resistant material, copper wires, FRP wire, carbon fibers, aramid fibers, etc. have been so far used.
For the practical purpose, it is desirable that the optical communication cable is light in weight and thin, and in this respect the aramid fibers are preferable as the tension-resistant material, but have such problems as high moisture absorption and high cost owing to the production route through solution spinning. High tenacity fibers of polyethylene may be used, but has such a problem as restriction to the processing temperature for forming a synthetic resin coating. In addition, the synthetic resin-based optical fibers have such a problem as increase of transmission loss due to the heat when the synthetic resin coating is formed by extrusion. It is necessary that the tension-resistant material works as a heat-insulating material between the optical fiber strand and the outer synthetic resin coating.